JP2746602B2 - Spectral filter - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention is for separating incident light in the visible region having a wavelength of 400 to 800 nm used in cameras, microscopes, optical measuring instruments and the like into transmitted light and reflected light. It relates to a spectral filter.

[Conventional technology]

This kind of spectral filter is generally called a half mirror, and conventionally, a transparent substrate made of glass or plastic is laminated with a metal thin film such as gold, silver, aluminum, or copper on one surface, or a transparent substrate similar to the above is laminated on one surface. To Ti
High refractive index dielectrics such as O ₂ , ZnS, ZrO ₂ and MgF ₂ , Na ₃ Al
It is known that a composite dielectric thin film composed of a dielectric having a low refractive index such as F ₆ and SiO _{2 is} laminated in several stages.

In these spectral filters, the ratio of the transmitted light and the reflected light to the incident light, that is, the visible light transmittance and the visible light reflectance, differs depending on each wavelength, and has a variation (distribution) in the entire visible region of 400 to 800 nm. doing. For this reason, the above-mentioned transmittance and reflectance are usually represented by an average value over the entire visible range, but this average value also varies depending on the type and thickness of the metal thin film or the composite dielectric thin film, and these factors are specified. When it is done, it will take a certain value.

Of course, the above average value is restricted within a limited range depending on which type of the spectral filter is used. In other words, in the type in which metal thin films are laminated,
The average value is in the range of visible light transmittance of 10 to 40% and the visible light reflectance is in the range of 60 to 90%. In the case of the type in which the composite dielectric thin film is laminated, the average value is in the range of visible light transmittance. The range is 30 to 80%, and the range of visible light reflectance is 20 to 70%. Therefore, conventionally, the range of use has been determined to some extent using the above-mentioned spectral characteristics as a guide.

[Problems to be solved by the invention]

However, each of the above-mentioned conventional spectral filters has a disadvantage that the dispersion of the visible light transmittance and the visible light reflectance in the entire visible region is too large. That is, the visible light transmittance has a central value in the entire visible range (400 to 800 nm) [(maximum transmittance + minimum transmittance) × 1/2], and the visible light reflectance has a central value in the entire visible range. For [(maximum reflectance + minimum reflectance) x 1/2], the variation exceeds ± 15% for each type with a laminated metal thin film, and ± 20% for each type with a composite dielectric thin film It had the above variations.

Such a variation causes a large hue difference between the incident light and the transmitted light and the reflected light. As a result, the transmitted light and the reflected light having substantially the same hue as the incident light (optical image) are generated. It cannot be obtained, and the spectral filter is greatly restricted in its use.

Therefore, according to the present invention, it is possible to obtain transmitted light and reflected light having substantially the same hue as the incident light with the above-mentioned small variation, and furthermore, to reduce the light absorption loss, that is, to make the incident light substantially the transmitted light. It is an object of the present invention to provide a spectral filter having excellent optical characteristics that can be divided into two parts with reflected light.

[Means for solving the problem]

The inventors of the present invention have conducted intensive studies to achieve the above object, and as a result, have found a spectral filter in which a laminated film having a San Germanti structure in which a metal thin film having a specific thickness is sandwiched between two dielectric thin films on a transparent substrate. For example, it is possible to obtain the transmitted light and the reflected light having substantially the same hue as the incident light by reducing the dispersion of the visible light transmittance and the visible light reflectance, and to obtain excellent optics with small light absorption loss. He knew that it could exert its characteristics, and completed this invention.

That is, the present invention relates to a film comprising a dielectric thin film as a first layer, a metal thin film having a thickness of 50 to 250 ° as a second layer, and a film made of the same material as the first layer as a third layer on one surface of a transparent substrate. A dielectric thin film having a thickness of 500 to 1,000 mm is laminated in this order, and the first and third dielectric thin films are made of Mg.
It is made of a dielectric material selected from F ₂ , SiO _x , SnO _x (all 0 <x ≦ 2), and ZnS, and the dispersion of the visible light transmittance over the entire visible region (400 to 800 nm) is the central value [( ± 12% or less with respect to [maximum transmittance + minimum transmittance) × 1/2], and the same variation in visible light reflectance is ± 12% with respect to the central value [(maximum reflectance + minimum reflectance) × 1/2] The present invention relates to a spectral filter for separating incident light into transmitted light and reflected light, which is characterized by the following.

This spectroscopic filter, by selecting the type of metal thin film and two dielectric thin films and the thickness within the above specific range, the average value of visible light transmittance and visible light reflectance over the entire visible range, various values, Generally, the above average value of visible light transmittance is
30-70% range, the above average of visible light reflectance is 30-70
%, And the average value is relatively wide, so that a spectral filter having a wide range of application can be provided.

In the following description, the visible light transmittance is the transmittance (T), the average value over the entire visible region (400 to 800 nm) is the average transmittance (Ta), and the center value [(maximum transmittance + minimum transmittance) Ratio) × 1/2] is abbreviated as transmittance distribution (Tσ), the visible light reflectance is the reflectance (R), and the average value over the entire visible range (400 to 800 nm) is the average reflectance ( Ra),
The variation with respect to the same central value [(maximum reflectance + minimum reflectance) × 1/2] is abbreviated as a reflectance distribution (Rσ).

[Structure and operation of the invention]

As the transparent substrate in the present invention, glass, polyester, polycarbonate, polyamide, polyimide, polyethylene, polyvinyl chloride, polyacrylic resin, polytetrafluoroethylene, sheets made of plastics such as triacetate, films, and other molded articles are used. The thickness is not particularly limited as long as transparency can be maintained, and is appropriately selected depending on the purpose of use.

This transparent substrate is subjected to an etching treatment or undercoat treatment such as sputtering, corona discharge, flame, ultraviolet irradiation, electron beam irradiation, chemical conversion, oxidation, etc. on its surface in advance,
The adhesion of the dielectric thin film or metal thin film provided thereon to the base may be improved. Before providing the dielectric thin film or the metal thin film, dust removal and cleaning may be performed by solvent cleaning or ultrasonic cleaning as necessary.

In the present invention, the first substrate is provided on one side with the first substrate.
A dielectric thin film was formed as a layer, a metal thin film was formed as a second layer, and a dielectric thin film similar to the above-mentioned first layer was formed as a third layer. That is, the metal thin film was sandwiched between two upper and lower dielectric thin films. It is characterized by forming a laminated film having a San de Germanite structure.

Here, as a material of the dielectric thin film constituting the first and third layers, a known metal oxide having a function as a dielectric,
Metal sulfides, metal fluorides, etc., of which those having a refractive index of 1.3 to 2.3 with respect to visible light and having a transmittance (T) of 50% or more, particularly 70% or more, per se Is preferably used.

As a typical dielectric material, a dielectric material selected from MaF ₂ , SiO _x , SnO _x (all 0 <x ≦ 2), and ZnS is used. These materials may be used alone or in combination of two or more.

As a method for forming the dielectric thin film, for example, there are a vacuum deposition method, a sputtering method, an ion plating method, a coating method, and the like, and an appropriate method may be employed depending on the type of the material and the required film thickness. it can.

The thickness of the dielectric thin film is not particularly limited in the first layer, and may have various thicknesses, but is preferably set in the range of 300 to 1,500 °. If it is too thin, it is difficult to form a continuous film. On the other hand, if it is too thick, cracks may occur, which is not preferable. On the other hand, in the third layer, it is preferable to set the range of 500 to 1,000 mm. If it is too thin, it is difficult to form a continuous film, and if it is too thick, the interference effect for each wavelength increases. Therefore, a spectral filter having a small transmittance distribution (Tσ) and a small reflectance distribution (Rσ) which are the objects of the present invention. Can not be obtained.

The provision of the first layer dielectric thin film greatly contributes to the improvement of the adhesion strength of the second layer metal thin film to the transparent substrate.
The thickness of the dielectric thin film of the layer may be the same or different. It can be appropriately selected according to the purpose of use of the spectral filter.

Further, as a material of the metal thin film constituting the second layer,
Gold (Au), silver (Ag), copper (Cu), aluminum (Al),
Any of various metals or alloys such as nickel (Ni), titanium (Ti), palladium (Pd) and tin (Sn) can be used. Among these, metals or alloys with low absorption loss of visible light are preferable, and particularly gold, silver,
Those made of copper, palladium or the like are preferable.

Examples of the method for forming the metal thin film include a vacuum deposition method, a sputtering method, an ion plating method, a gas-phase plating method, a chemical plating method, an electric plating method, a chemical coating method, and a combination method thereof. The vacuum deposition method is most preferable in terms of film uniformity, formation speed, and workability.

It is necessary to set the thickness of the metal thin film in the range of 50 to 250 °, and particularly preferably in the range of 80 to 200 °. If the thickness is less than 50 °, the transmittance (T) becomes high, but the reflectance (R) becomes too low, and if the absorption loss of light becomes high, other defects such as oxidation stability and the like are impaired. Optical characteristics cannot be obtained. On the other hand, if it exceeds 250 °, the transmittance (T) becomes extremely low, so that it is not suitable for use as a spectral filter.

Thus, in the present invention, a dielectric thin film as a first layer, a metal thin film of a specific thickness as a second layer, and a dielectric thin film of a specific thickness as a third layer are sequentially formed on one surface of a transparent substrate. Although such a laminated film is formed, a change in behavior such as light scattering, interference, transmission, and absorption occurs when compared to the case of using a metal thin film alone, and this change is caused by the transmittance (T) and the reflection. By acting to reduce the wavelength dependence of the rate (R), a special action and effect that the transmittance distribution (Tσ) and the reflectance distribution (Rσ) are significantly reduced is achieved.

That is, with the above film configuration, both the transmittance distribution (Tσ) and the reflectance distribution (Rσ) are ± 12% or less, particularly preferably ± 10% or less. In this case, the transmitted light and the reflected light are less than the incident light. It has almost the same hue. Moreover, according to the above configuration, light absorption loss is reduced,
The incident light can be roughly divided into transmitted light and reflected light, and a desirable result can be obtained in terms of the efficiency of using the separated light.

Furthermore, in the above configuration, the upper and lower dielectric thin films, particularly the upper dielectric thin film, also function as a protective film for the metal thin film as the intermediate layer, and as a result, the wear resistance of the conventional metal thin film alone, Solvent resistance, chemical resistance, heat resistance, and the like are improved, and there is also an advantage that a spectral filter having extremely excellent durability can exhibit stable spectral characteristics.

As described above, the average transmittance (Ta) and average reflectance (Ra) of this spectral filter vary depending on the type and thickness of the metal thin film or the dielectric thin film, but generally, the average transmittance (Ta) Is in the range of 30 to 70%, particularly preferably in the range of 40 to 60%, and the average reflectance (Ra) is in the range of 30 to 70%, particularly preferably 40 to 60%.
%, And can be arbitrarily selected within this range according to the specific purpose of use.

In the spectral filter of the present invention, a transparent hard coat layer made of an organic substance or an inorganic substance may be further provided as necessary on the third dielectric thin film in order to improve the scratch resistance of the film. Good.

〔The invention's effect〕

As described above, according to the present invention, the transmittance distribution (T
σ) and the reflectance distribution (Rσ) are both small, so that transmitted light and reflected light having substantially the same hue as the incident light can be obtained, and further, light absorption loss is small, and spectral durability is excellent. A filter can be provided.

In addition, this spectral filter can set the average transmittance (Ta) and average reflectance (Ra) arbitrarily within a relatively wide range, and requires only the sequential lamination of a metal thin film and a dielectric thin film above and below it. Therefore, since the optical characteristics can be improved as described above, it is advantageous in terms of productivity and cost as compared with the conventional one in which the composite dielectric thin film is provided.

For this reason, the spectral filter of the present invention can reduce the incident light p by setting the incident angle of light to 90 degrees or less (usually about 45 degrees) in addition to optical instruments such as a camera, a microscope, and an optical measuring instrument.
-Component and s- component can be used as a polarization beam sputter (polarization separator) that separates the component at 90 degrees with almost no loss.
Application to the other side of video disks, optical memories, optical communications, and the like using light becomes possible.

〔Example〕

Hereinafter, embodiments of the present invention will be described in more detail. The measurement of the transmittance (T) and the reflectance (R) shown below was performed using a spectrophotometer UV-240 manufactured by Shimadzu Corporation.
This is done using.

Example 1 After evacuating the inside of a bell jar to 1-2 × 10 ^-4 Torr, a 100 μm-thick polyester film set on a tungsten board at a distance of about 20 cm from an evaporation source by ZnS charged by a resistance heating method. Vacuum deposition was performed on one surface at a deposition rate of several Å / sec to form a first layer of a ZnS thin film having a thickness of 600 Å.

Next, on this first layer, Ag was vacuum-deposited by a resistance heating method under the conditions of a degree of vacuum of 1 to 2 × 10 ⁻⁴ Torr and a deposition rate of several tens of degrees / second to form an Ag thin film having a thickness of 120 °. Was formed. Further, on this second layer, ZnS is again vacuum-deposited by the same operation as above to form a third layer of a ZnS thin film having a thickness of 600 °, and a spectral layer on the film having the structure shown in FIG. 1 is formed. I got a filter.

In FIG. 1, 1 is a transparent substrate made of a polyester film, 2, 4 are dielectric thin films made of ZnS, and 3 are metal thin films made of Ag.

In order to investigate the optical characteristics of this spectral filter, the transmittance (T) and the same reflectance (R) in the entire visible range (400 to 800 nm) are used.
Was measured. The result is shown in FIG. In the figure, the solid line −
a ₁ is the transmittance (T), the dotted line -b ₁ is a reflectance (R).

From FIG. 2, it can be seen that the transmittance (T) is 40 to 48 over the entire visible range.
%, The variation with respect to the central value [(40 + 48) × 1/2], that is, the transmittance distribution (Tσ) is as small as ± 4%, and the reflectance (R) is 52 to 60% in the entire visible region. It can be seen that the variation with respect to the central value [(52 + 60) × 1/2], that is, the reflectance distribution (Rσ) is as small as ± 4%. Further, from FIG. 2, it is clear that the incident light is substantially divided into the transmitted light and the reflected light, and the light absorption loss is small. The spectral filter has an average transmittance (Ta) of 44% and an average reflectance (R
a) was 55%.

Next, in Example 1 described above, a plurality of spectral filters having different average transmittances (Ta) and average reflectances (Ra) were prepared by changing the thickness of the Ag thin film of the second layer in various ways. When the film thickness is in the range of 50 to 250 °, both the transmittance distribution (Tσ) and the reflectance distribution (Rσ) are within ± 10%, the light absorption loss is small, and the durability such as oxidation stability is high. It was confirmed that it was excellent.

On the other hand, when the film thickness is less than 50 mm, the average reflectance (Ra) becomes too low, the light absorption loss increases, the durability such as oxidation stability is poor, and the film thickness exceeds 250 mm. When the average transmittance (Ta) becomes too low, problems begin to occur. In order to avoid these problems and to provide characteristics suitable as a spectral filter, the average transmittance (Ta) should be set in the range of 50 to 250 °. It was confirmed that there was.

Comparative Example 1 A comparative spectral filter was prepared in the same manner as in Example 1 except that the first and third dielectric thin films made of ZnS were not formed, and only the Ag thin film having a thickness of 120 ° was provided. The optical characteristics of this spectral filter were examined in the same manner as in Example 1. The result is shown in FIG. In the figure, a solid line -a ₂ transmittance (T), the dotted line -b ₂ denotes a reflectance (R).

From FIG. 3, the transmittance (T) is 22 to 57 over the entire visible range.
%, The variation with respect to the central value [(2257) × 1/2], that is, the transmittance distribution (Tσ) is as large as ± 18%, and the reflectance (R) is 40 to 78% in the entire visible region. It can be seen that the variation with respect to the central value [(40 + 78) × 1/2], that is, the reflectance distribution (Rσ) is as large as ± 19%.

In addition, it has been found that this spectral filter does not have a dielectric thin film, and thus has poor durability and has difficulty in exhibiting stable spectral characteristics. The average transmittance (Ta) and average reflectance (Ra) of the spectral filter were 37.5% and 62.5%, respectively.

Example 2 A spectral filter was manufactured in the same manner as in Example 1 except that the thickness of the first layer of a dielectric thin film made of ZnS was changed to 500 °. When the optical characteristics of this spectral filter were examined in the same manner as in Example 1, the range of the transmittance (T) was 35
5353%, the transmittance distribution (Tσ) is ± 9%, the reflectance (R) range is 47-65%, and the reflectance distribution (Rσ) is ± 9%.
%. The spectral filter had an average transmittance (Ta) of 47% and an average reflectance (Ra) of 53%.

Examples 3 and 4 The same procedure as in Example 1 was repeated except that the thickness of the third dielectric thin film made of ZnS was changed to 500 ° (Example 3) and 1,000 ° (Example 4). A spectral filter was prepared. The optical characteristics of each spectral filter were examined in the same manner as in Example 1. The results are shown in Table 1 below.

Comparative Examples 2 to 5 The thickness of the third layer of the dielectric thin film made of ZnS was changed to 200 ° (Comparative Example 2), 300 ° (Comparative Example 3), 1,500 ° (Comparative Example 4), and 2,000 ° (Comparative Example 5). Example 1 except for the change
In the same manner as described above, four types of spectral filters were produced. The optical characteristics of each spectral filter were examined in the same manner as in Example 1. The results are shown in Table 1 below.

As is clear from the results in Table 1 above, the spectroscopy of Examples 3 and 4 in which the thickness of the third dielectric thin film made of ZnS was set to 500 to 1,000 °, which is within the range of the present invention. The filter has a transmittance distribution (Tσ) and a reflectance distribution (R
σ) is suppressed to ± 12% or less,
In the spectral filters of Comparative Examples 2 to 5 in which the film thickness was outside the above range, one or both of the above distributions had a value exceeding ± 12%, and the hue was almost the same as that of the incident light as the object of the present invention. It can be seen that transmitted light and reflected light are difficult to obtain.

Example 5 First and third dielectric thin films were each formed of SiO _x (0
A spectral filter was produced in the same manner as in Example 1 except that the spectral filter was changed to that of <x <2). When the optical characteristics of this spectral filter were examined in the same manner as in Example 1, the range of the transmittance (T) was 35 to 43%, the transmittance distribution (Tσ) was ± 4%, and the reflectance (R ) Ranges from 57 to 65
%, The reflectance distribution (Rσ) was ± 4%. The spectral filter had an average transmittance (Ta) of 40% and an average reflectance (Ra) of 59%.

Example 6 A spectral filter was produced in the same manner as in Example 1 except that the second metal thin film was changed to a layer made of Al having a thickness of 130 °. When the optical characteristics of this spectral filter were examined in the same manner as in Example 1, the transmittance (T) range was
35 to 39%, the transmittance distribution (Tσ) is ± 2%, the reflectance (R) range is 53 to 61%, and the reflectance distribution (Rσ) is ± 2%.
It was 4%. The average transmittance (Ta) of this spectral filter was 37%, and the average reflectance (Ra) was 56%.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of the spectral filter of the present invention, FIG. 2 is a characteristic view showing optical characteristics of the spectral filter of Example 1, and FIG. 3 is a characteristic showing optical characteristics of the spectral filter of Comparative Example 1. FIG. 1 ... Transparent substrate, 2,4 ... Dielectric thin film, 3 ... Metal thin film

Claims (2)

(57) [Claims] 1. A transparent base material having a dielectric thin film as a first layer, a metal thin film having a thickness of 50 to 250 ° as a second layer, and a film made of the same material as the first layer as a third layer on one surface of a transparent substrate. 500-1,0
And a first and third dielectric thin films formed of MgF ₂ , SiO _x , and SnO _x.
(Both 0 <x ≦ 2), made of a dielectric material selected from ZnS, in the visible region of visible light transmittance (400 to 800 nm)
The variation in the whole area is the central value [(maximum transmittance + minimum transmittance)
× 1/2] or less and ± 12% or less with respect to the central value [(maximum reflectance + minimum reflectance) × 1/2]. A spectral filter for separating incident light into transmitted light and reflected light. 2. The method according to claim 1, wherein the average value of the visible light transmittance in the entire visible region (400 to 800 nm) is in the range of 30 to 70%, and the average value of the visible light reflectance is in the range of 30 to 70%. The spectral filter according to 1).